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Transcript of E.D.D. Dimensioning
Tristan Smith Placement of Dimensions Standardized by ANSI and the ISO (Int'l Organization for Standardization)
U.S. drawings are dimensioned in one of the following:
Two systems of dimensioning (you can use either one)
Aligned system - Dimensions read from bottom and right side of any view; numbers are perpendicular to their respective dimension lines
Unidirectional system - Dimensions only read from the bottom; all numbers placed horizontally Aligned System Unidirectional System First off, a drawing must contain the following views:
Only ONE dimension line per feature (edge, circle diameter, etc.)
Therefore, for each feature, the dimension line is placed on the view that displays it BEST
Dimensions placed between views and outside of object whenever possible
Add overall height (H), length (L), and depth (D) of the entire view and for each detail
The smaller the dimension, the closer it is to the view
NEVER place dimensions so that they are read from the top and/or from the left of the drawing (only bottom and right)
If dimensions are parallel:
All should be on the same plane
Leave one out
Stagger the dimension numbers so they are read better
Numbers go in middle of dimension line whenever possible
If all dimension lines are parallel, have one reference dimension (indicated using parentheses)
If dimension is less than half an inch, place dimension lines outside of extension, with arrows pointing in.
If you are unsure if a dimension should be added, add it
Don't place dimensions on the view itself unless it provides clarity
Don't dimension hidden lines
Don't duplicate a dimension Proper Placement of Numbers, Letters, and Fractions Letters and numbers: 1/8in. high
Fractions: 1/4in. high
Numbers that make up the fractions: 3/32in. high
Fraction bar: Drawn horizontally (using instruments); numbers cannot touch bar
Always use a soft lead (H, 2H, .5, etc.)
Know how to convert fractions to decimals and vice versa Rules for Dimensioning a Drawing Extension lines may cross visible object lines.
Extension lines may cross other extension lines; they may not cross dimension lines.
Always maintain a visible space of a approximately 1/16" between the object and the extension line.
Extension lines should terminate 1/8" past the last dimension line.
Center lines often serve as extension lines when dimensioning round symmetrical surfaces.
Always leave a space of no less than 3/8" between the object and the first dimension line.
Dimension lines beyond the first should be no closer than 1/4" to each other.
Arrowheads are drawn 1/8" to 1/4" long, depending on the drawing size, and have a width equal to approximately 1/3 of the length. •The coordinate method
When a high degree of accuracy is needed
Uses distance instead of angles
for more accuracy we split the degree into minutes and seconds
The number is always followed by the degree symbol. Dimensioning Angles Inclined Surfaces – Rounded corners and arcs are dimensioned as radii in their rounded views,
with “R” preceding the dimension.
– Arcs greater than 180º are dimensioned with the diameter. Arcs less than
180º are dimensioned with the radius.
– Dimension to the center of an arc, rather than the outermost edge Dimensioning ARCS A: When possible, use a leader line.
If it will improve clarity of the drawing, dimensioning directly on the circle is acceptable.
B: Always locate the center of a hole in relation to a corner.
Dimensioning multiple circles, they may be located from center to center.
Repetitive features or dimensions may be specified by giving the required number of features and an "x", followed by the size dimension.
C: When dimensioning holes, giving both the diameter and the depth may be necessary.
The abbreviation "THRU" indicates a hole that passes all the way through an object Rules for Dimensioning Circles and Holes. Size and Location Dimensions •When dimensioning a drawing, always give the size and location dimension of every feature.
•Size dimensions give the size of the basic geometric shapes and forms.
•location dimensions locate these basic shapes with respect to each other.
•always include the height, length, and depth of every detail. Alex is the Best Leader Lines •Leader lines are thin inclined lines used to direct a dimension, note or symbol to the dimensioned surface
•Leader Lines can be drawn on any angle from 30 Degrees to 60 degrees
•They have a short horizontal shoulder that is 1/4'' long
•Never allow leader lines to cross dimension lines. they may cross visible object lines and extension lines
•When leader lines are used to dimension a Radius or diameter, the arrowhead should touch the circumference, and point to the midpoint of the arc of the Circle. Alex is the Best Rules For Dimensioning Circles & Holes (Cont.) D: If several circles are to be dimensioned, they may be located by dimensioning from center to center.
E:Sometimes equally spaced
F:Cylinders are to be Dimensioned on the Rectangular view.
G:Partial views may be used to describe cylindrical objects only if both halves are identical
H:When dimensioning holes along with giving the diameter, it may be necessary to give the depth and number of holes required( in that order). The abbreviation TRU maybe used to indicate a hole
I: A hole that does not pass all the way through an object is referred to as a blind hole.
J: If only one hole is to be dimensioned, the number of holes required. THE END